Alerting system

ABSTRACT

An aircraft cockpit display system for indicating whether the aircraft is above, below, within or adjacent to a preset altitude corridor. The binary coded decimal output of an altitude reporting encoder is combined with a signal indicative of the assigned altitude preselected by thumbwheel switches. The computed deviation from the command altitude is compared to a similarly selected deviation setting. A deviation detection logic unit provides output signals to shape-coded, lightable indicators advising the pilot to descend or climb to the flight corridor, if necessary. A proximity detection logic unit receives signals from the deviation detection logic unit and an adjustable proximity range selector indicative of proximity zones above and below the flight corridor to drive an indicator and audio beeper to alert the pilot of approaches to and departures from the flight corridor.

[54] ALERTING SYSTEM [72] Inventors:

Kalatucka, Willow Grove, both of Pa.

The United States of America as represented by the Secretary of the NavyFiled: Dec. 18, 1970 Appl. No.: 99,563

[73] Assignee:

[56 1 References Cited UNITED STATES PATENTS 3,217,293 11/1965 Metz..340/l46.2 3,355,706 I 11/1967 Pitches ..340/27 R 3,273,122 9/1966Chandler. ...340/l46.2 3,538,316 11/1970 Barrett et a1.

John M. K. Bergey, Doylestown; Stephen 3,237,159 2/1966 Emmons...340/l46.2

Primary Examiner-Malcolm A. Morrison Assistant Examiner-James F. GottmanAnorne vR. S. Sciascia, Henry Hansen and Gilbert H. Hennessey [5 7]ABSTRACT An aircraft cockpit display system for indicating whether theaircraft is above, below, within or adjacent to a'preset altitudecorridor. The binary coded decimal output of an altitude reportingencoder is combined with a signal indicative of the-assigned altitudepreselected by thumbwheel switches. The computed deviation from thecommand altitude is compared to a similarly selected deviation setting.A deviation detection logic unit provides output signals to shape-coded,lightable indicators advising the pilot to descend or climb to theflight corridor, if necessary. A proximity detection logic unit receivessignals from the deviation detection logic unit and an adjustableproximity range selector indicative of proximity zones above and belowthe flight corridor to drive an indicator and audio beeper to alert thepilot of approaches to and departures from the flight corridor.

12 Claims, 5 Drawing Figures POSITlVE ALT.

ADDITION UNIT DEVIATION DETECTION LOGIC UNlT PROXIMITY DETECTION LOGICUNIT July 25, 1972 ALTITUDE PATENTEDJUL25 m2 LOWER FLIGHT UPPER APPROACHCORRIDOR) CORRIDOR [APPROACH CORRIDOR SHEET 1. OF 3 fig. 1.

n: a: go as s LU." z I Lu f 5 m 9 o 2 5 I v a PROXIMITY SETTING Q MAriDDEVIATION SETTING A LT IT U DE DEVIATION SETTING PROXIMITY SETTINGINVESTORS JOHN M. K. BERGEY STEPHEN KALATUCKA ALERTING SYSTEM STATEMENTOF GOVERNMENT INTEREST The invention described herein may bemanufactured and used by or for the Government of the United States ofAmerica for governmental purposes without the payment of any royaltiesthereon or therefor.

BACKGROUND OF THE INVENTION The invention relates generally to thefields of altimetry and digital comparators, and more particularly toimproved logic systems for alerting a pilot of his position relative toa plurality of selected altitude corridors.

Due to the hazards of increased air traffic, there is substantialagreement in the aviation community that altitude awareness must beincreased. Pilots often are not immediately aware of dangerousdeviations from assigned altitudes. Previous analog systems employingsynchro pickoffs from an altitude responsive member were not easilyadjustable, required periodic adjustments and interfered with thealtimeter reading to some degree. In many prior art devices the centeraltitude of the flight corridor could be manually set, but the width ofthe corridor was not adjustable. Nor was the pilot automaticallynotified of approach to and departure from the corridor.

SUMMARY OF THE INVENTION Accordingly, one of the objects of theinvention is to increase altitude awareness by advising the pilot ofapproaches and deviations from a preselected altitude. Another object ofthe invention is to improve the versatility and accuracy of altitudealerting systems by enabling simple manual selection of flight corridorparameters such as assigned altitude and permissible deviations. Afurther object of the invention is to use the digital outputs of analtitude reporting encoder to derive information relative to settablereference altitudes. Still another object of the invention is to displayinformation relating to assigned altitudes in a compact, easily readableform.

These and other objects of the invention are achieved by providing a setof shape-coded indicators operated by a digital logic system whichautomatically decides whether an aircraft is above, below, within oradjacent to a selected altitude corridor. A logic unit combines the.indicated altitude in binary coded decimal form from an altitudereporting encoder with a thumbwheel selected command or assignedaltitude to generate a digital altitude error signal which is comparedin a deviation detection logic unit to a selected deviation range. Theoutput of the deviation detection logic unit drives shapecoded,lightable indicators advising the pilot to descend or climb to theassigned corridor, if necessary. A proximity detection logic unitcompares the output of the deviation detection logic unit with aselected proximity range indicative of proximity zones or approachcorridors above and below the flight corridor to alert the pilot ofapproaches to and departures from the flight corridor.

BRIEF DESCRIPTION OFTI-IE DRAWINGS FIG. -I is a perspective view of anembodiment of the altitude advising and alerting display according tothe invention;

FIG. 2 is a block diagram of the logic circuitry associated with thedisplay of FIG. 1;

FIG. 3 is a block diagram of an embodiment of the addition unit of FIG.2;

FIG. 4 is a blockdiagram of an embodiment of the deviation and proximitydetection logicunits of FIG. 2; and

FIG. 5 is a truth table for the display of FIG. I additionally showingthe vertical arrangement of altitude corridors.

DESCRIPTION OF THEPREFERRED EMBODIMENTS An altitude advising andalerting display module designed to be mounted on an aircraft instrumentpanel is depicted in FIG. 1 to illustrate the general appearance of thedisplay according to the invention. A digital altitude display 12 iscomposed of six elements driven by a suitable altimeter and digitalencoder such as that described in the copending U.S. Pat. ApplicationSer. No. 625,921 filed Mar. 22, I967 for Readout Device for AltitudeReporting Encoder" by John M. K. Bergey now U.S. Pat. No. 3,560,959issued Feb. 2, l97l. In accordance therewith the first element 13 is aminus sign, termed negative altitude discrete, which may be activated bythe encoder system to display barometrically uncompensated altitudesindicated to be below sea level. The next three elements l4, l5 and 16are seven segment decimal displays for the l0,000s, 1,000s and 100sdigits respectively. The last two elements 17 and l8are dummy zeros forthe 10s and ones digits, resolution being limited to one hundred footincrements. The altitude alerting display comprises three shape-coded,lightable indicators arranged about altitude display 12. A descentindicator 2| in the form of a large downward arrow-is located directlyabove the center of display 12. Likewise, an arrow-shaped ascentindicator 22 is located opposite indicator 2] below display 12. Directlyto the left of display I2, there is a confirm or bull's-eye" indicator23.

Referring now to FIG. 2, the logic system operating indicators 21, 22and 23 of the altitude alerting display 24 employs inputs from twosources. One group of inputs is from a manual selection unit 26comprising three thumbwheel setting units for adjusting variousparameters of the flight corridors. The other group of inputs representsthe indicated altitude in binary coded decimal (BCD) units received froma suitable altimeter encoder such as that shown in the above-mentionedcopending application. By analyzing these two groups of inputs, thelogic system determines which indicators in display 24 should beactivated.

A command altitude setting unit 27 comprising three thumbwheel switches28, 29 and'3l is used to set in the assigned or commandaltitude. All ofthe thumbwheel switches described herein are mechanically similar andcomprise a manually rotatable wheel with a gear driven display of theappropriate decimal digit 0 through 9 and an encoder to convert thedecimal to a four-digit natural binary number. Many suitable types ofcommercial thumbwheel encoders are available. For example, by contactinga series of conductive strips arranged in four concentric circulartracks on a disc rotatable with the thumbwheel, four correspondingelectrical pickoffs could sense the appropriate binary status of thestrip for any given location on a particular track. The binary outputthus consists of four parallel lines and represents the regular orinverted binary digits depending on the signal levels employed.

For command altitude setting unit 27 thumbwheel switches 28, 29 and 31represent respectivelythe 10,000 feet, l,000 feet and I00 feet digit inthe assigned altitude.

Referring now to FIG. 3 addition unit 32 is implemented to generate thedifference between the indicated altitude and the command altitude intwo's complement BCD form by adding the indicated altitude and the two'scomplement of the command altitude established by setting unit 27. EachBCD unit forming the indicated output is passed to a respective four bitbinary full adder. In particular, the 100 feet unit comprising fourbinary digits 'of the indicated altitude is passed to a full adder 35.In FIG. 3 these inputs are given the conventional notation 800, 400, 200and I00 respectively representing the may be summed. The outputs fromthumbwheel switches 28,

29 and 3l are inverted by choice of signal level thus providing the onescomplement of the command altitude in BCD form. To yield the two'scomplement of the command altitude, however, a binary one is hard-wiredto the least significant carry input in full adder 35. The twoscomplement of the command altitude is thus automatically provided forsumming with the indicated altitude. It is well known that the sum of afirst binary number and a second binary number in two's complementbinary form yields a binary numberalso in twos complement form equal tothe difference between the first and second numbers and the proper signof that difference. Adders 35, 36 and 37 could be thought of as aregular l2-bit full adder but for the fact that the BCD form instead ofstraight natural binary is being used. These adders do, however, operatein the conventional manner with carry over from one sum bit to the moresignificant bit. The final adder 37 has a most significant carry outputC,, meaning command carry, which indicates'the signof the differencebetween the indicated and command altitudes. When C, is a ,one," theindicated altitude is greater than or equal to the command altitude.Otherwise the command altitude is greater than the indicated altitud,e.An inverter 38 provides the complement of C,, C,, useful in theremainder of the circuit.

To yield a valid BCD code the generated sum must be operated on by acorrection circuit 39. The sum outputs from full adder 35 are passed toanother full adder 41 where each of the 4 bits from adder 35 is summedwith an appropriate correctiondigit. The ,least significant bit fromadder 35 is summed with a hard-wired binary zero. The most significantcarry from adder35 is passed along with the command carry, C,, to anexclusive OR gate 42 whose output is passed to adder 41 to be summedwith the second bit of adder 35. The complement of the command carry,C,, is passed along withthe output of exclusive OR gate 42 to AND gate43 whose output is summed with the third bit of adder35. C, and theoutput of exclusive OR gate 42 are ANDed in gate 44 whose output issummed with the most significant sum bit of adder 35. It should be notedthat adder 41 has a hard-wired binary zero input to its leastsignificantcarry stage. The sum output of adder 36'is similarlycorrected by another full adder 46. The manner in which the bits aresummed in the adder 46 is exactly the same as in adder 41. A

Addition unit 32 thus provides two groups of outputs: one group relatedto thesignof the difference indicated by C, and itscomplement and theother group representative of the difference between the indicated andcommand altitudes. This latter'output is in valid BCD twos complementform and comprises twelve Iines divided into three groups of fourrepresenting the 10,000 feet, 1,000 feet and 100 feet unit.

The output of addition unit 32' is passed to a deviation detection logicunit '47 (FIG. 2) and combined with the corresponding outputs of adeviation setting unit 48 in selection unit 26. The deviation setting isdefined as the permissible vertical deviation from the command altitudeand thus establishes the height of the flight corridor. Two thumbwheelswitches 49 and 51 are used to set in the desired l,000,feet and 100feet digit for the deviation setting. Deviation settings up to 8,900feet on either side of the command altitude are possible.

The general function of deviation detection logic unit 47 is todetermine by comparison with the selected deviation tolerance whether adifference between the indicated and command altitudes places theaircraft above, below, or within the established flight corridor. Thus,one output of unit 47 indicates that the aircrafl is too high,activating descend indicator 21. A second output is passed to an OR gate52 to activate confirm indicator 23. A third output of unit 47 indicatesthat theaircraft is too low, lighting ascend indicator 22. If the. C,output from addition unit 32 is a binary (indicated less than commandaltitude), the deviation setting as provided by thumbwheel switches 49and 51 is added directly in straight BCD form to the sum output ofunit32; on the other hand, if C, =l the one's complement of thedeviation setting must be used. Normally this requirement wouldnecessitate using a string of exclusive OR gates since the requiredcoding (true or complement) of thedeviation setting is a function of C,.However, through the unique, use of BCD thumbwheel switches havingcommon complementary leads, the coding of thejswitches is directly,logically controllable via the C, and the,C,- signals. For example, ametallic conductive track encoder for the thumbwheel switch could havetwo sets of conductive strips oneach track corresponding respectively toa tively connected to the other set of strips. When C, is 1", C,

is "0" and th e first set of strips would be high..0n the other hand.when C, is 0", C is ,l and-the'othersetof strips would be high. As aresult, only one set of four leads is provided from each thumbwheelswitch and additional logic is unnecessary. The encoder track strips areconnected so that when C, is l, the true form of the-deviation settingis provided and when C, is O," the one's complement of the deviationsetting is provided. I

Referring to FIG. 4, deviation detection logic unit 47 includes threefull adders 53, 54 and 55. Adders 53 and 54 sum corresponding units fromunit 32 and thumbwheel switches 49 and 51 in the true or complement formasdetermined by the value of C,. A binary 0" is hard-wiredto the-leastsignificant carry input of adder 53. Adder 55 sums C, with each of thefour ,most significant bits in the sumoutput of unit 32. The mostsignificant carry bit of full adder 55 is designated deviation carry CIt is used in conjunction with C, and the positive altitude discreteprovided by an altitude reporting encoder to generate HIGH, 15mm (i.e.,within the flight corridor) and LOW signal outputs. The Booleanequations describing these signals are as follows:

HIGH C, C POSITIVE'ALTITUDE DEVIA I E (C,$C POSITIVE ALTITUDE, and

LOW e; c mammmmm:

The HIGH, DEVIAIE, and LOW signals activate descend, confirm and climbindicators 21, 23 and 22, respectively. The above equations areimplemented by an AND gate 61 whose inputs are positive altitudediscrete, C, and C,,, where C,, is obtained from the carry output ofadder 55 and C, from the carry output of adder 37 in addition unit 32.The output of AND 52 to activate confirm indicator 23. To light ascendindicator 22, an AND gate 64 with inputs C and C, provides one input toan OR gate 65. The other input is the complement of' the positivealtitude discrete provided by an inverter 66. C is provided by aninverter 67 connected to the carry line for C, The

outputs from full adders 53, 54 and 55 are designated! through 2, where2, through 2 2, through 2., and 2, through 2,, correspond to the feet,L000 feet, and'l0,000 feet units respectively. I

Referring briefly again to FIG. 2, a proximity detection logic unit 7lreceives the sum output of deviation detection logic unit 47. C, and C,,positive altitude discrete and a logically controlled proximity settingfor the I00 feet unit.'The output of proximity detection logic unit 71forms the other input to OR gate 52 whose output actuates confirmindicator 23. The output of logic unit 71 may also be connected to anaudio beeper 72 to provide an audiblesignal of approach to or de parturefrom the flight corridor. A proximity settingunit 73 in 7 53 indeviation detection logic unit 47 designated 2, through E, is firstcorrected, if necessary, for-an invalid BCD 'code.-As in addition unit32, this is accomplished via gating and a four bit full adder.Correction unit 75 in proximity detection logic unit 71 operates in thesame manner as correction unit 39 in addition unit 32 except thatcorrection is only needed for the 100 feet unit. If C, 0, i through 2,,must all be ls," while if the indicated altitude is greater than orequal to the command altitude and C,.= l 2, through 2 must all be s.These conditions are checked via two eight input AND gates 77 and 78,the input to gate 77 being inverted via eight inverters symbolized byinverter 79. The logically controlled proximity setting unit 73 outputis added in a four bit full adder 81 to the corrected 100 feet unit sum.The least significant carry in of adder 81 is connected to receive C,.The proximity carry, C,,, the most significant carry output of adder 81,is monitored along with the eight input AND gate signals to determine ifa proximity signal should be generated. The applicable Boolean equationis as follows:

PROXlMlTY gai -2 2 ig-5832792615) ((7.223 ii wu' a' u' v' a' s) Theproximity signal, like the DEVlATE signal, is used to activate confirmindicator 23. To complete implementation, a first AND gate 82 receivesthe positive altitude discrete, the output of AND gate 77 and thecomplement of C, provided by an inverter 83. A second AND gate 84receives the output of AND gate 78, signal C, and the positive altitudediscrete. The outputs of AND gates 82 and 84 are ORed together in gate86 whose output is passed to OR gate 52 in FIG. 2 activating confirmindicator 23.

The general operation of the alerting system can best be understood byreference to FIG. 5, a combination truth table and graphicalrepresentation of the corridor arrangement. The vertical dimensionrepresents altitude and the shaded portion indicates the desired commandflight corridor. Assigned to a specific altitude, the pilot may set inthe assigned altitude by rotating the thumbwheel switches in commandaltitude setting unit 27 to the appropriate numbers. At the same time atolerance range above and below the command altitude is established byadjusting deviation setting unit 48, thus setting the height of theflight corridor. If the actual (i.e., indicated) aircraft altitude iswithin this corridor, only confirm indicator 23 is activated. To alertthe pilot to approaches and departures from the flight corridor,proximity zones termed approach corridors adjacent to and above andbelow the flight corridor may be set in by proximity setting unit 73.When the aircraft is within the upper approach corridor, both thedescend and confirm indicators are activated. Likewise, if the aircraftis in the lower approach corridor, the ascend and confirm indicators areactivated. An audible signal can also be produced by beeper 72 (FIG. 2)while the aircraft is passing through either approach corridor. If theaircrafi is above the upper approach corridor, the descend indicatoralone is activated; and if it is below the lower approach corridor, onlythe ascend indicator is lit. if the proximity setting is zero, the threeindicator signals are mutually exclusive since confirm indicator 23 isonly active when the indicated altitude is in the following range:command altitude minus deviation indicated altitude 5 command altitudeplus deviation. If the deviation setting is zero, then the only timeconfirm indicator 23 alone is energized is when the indicated altitudeis exactly equal to the command altitude.

The functioning of the altitude alerting system is deliberatelyuncomplicated to facilitate quick comprehension by pilots. Yet the logicrequired to implement these functions is relatively complex due to thefact that there are 900 million independent input combinationsassociated with the variable indicated altitude and the commandaltitude, deviation and proximity settings.

In order to understand the operation of the logic implementation,several different typical situations will be described. If the indicatedaltitude from an altitude reporting encoder is negative only the ascendindicator is activated. This can easily be understood from FIG. 4 inwhich gates 61, 63, 82 and 84 are all inhibited by a negative altitudereading, that is, a 0 for the positive altitude, while OR gate 65 alonehas an output for a negative altitude discrete. Let us assume now thatthe altitude is positive but well below the flight con'idor and lowerapproach corridor. At this point the indicated altitude would be addedto the two's complement of the command altitude as provided by commandaltitude setting unit 27. If the command carry, C is 0" and the mostsignificant carry from full adder 36 (FIG. 3) designated C is 0 theassociated exclusive OR gate will have no output and the correctionlogic for the sum output of adder 36 will be effectively inhibited. ifon the other hand, C is l the binary number 0] 10 will be added to the1,000 feet sum from adder 36 by the correction circuitry of unit 39 toyield a valid BCD unit. Similarly if the most significant carry, C foradder 35 is l and C is 0, the binary number Ol 10 will be added to the100 feet sum by the correction circuitry of unit 39. Next the unitsprovided by deviation setting unit 48 are added to the eight leastsignificant bits of the addition unit 32 output, which is still in thetwos complement form. The purpose of this operation is to compare thealtitude error with the permissible deviation. if at this point thedeviation carry, C is 1" confirm indicator 23 is lit via exclusive ORgate 62 since we have assumed C, is 0". On the other hand, if C,, is 0,"climb indicator 22 is activated via AND gate 64. Since we are assuming avery low indicated altitude, C is 0" and indicator 22 would beactivated. The proximity condition would not be satisfied. First, ANDgates 77 and 78 (FIG. 4) would test 2 through 2, to determine whetherthey were all ls. If they were not, this in itself would indicate thatthe proximity zone had not been reached. If they were all l s, the 100feet unit sum from adder 53 in logic unit 47 would be checked. lf the100 feet unit carry C' is 0 the exclusive OR gate in correction unit 75has no output and no correction takes place. However, if C' is l thebinary number 0110. is added to the 100 feet sum for correction to avalid BCD code. At this point the proximity setting from unit 73 isadded to the corrected 100 feet sum and the carry for the mostsignificant bit is monitored. If C,,, the proximity carry, is 0, ANDgate 84 is inhibited, indicating that the lower proximity or approachcorridor has not been reached. However, if C, were l AND gate 84 wouldproduce an output to light confirm indicator 23 at the same time asclimb indicator 22, thus alerting the pilot of the proximity situation.

Where the indicated altitude is greater than or equal to the commandaltitude, the command carry, C,., is I. If, in addition unit 32, the Ccarry from full adder 36 is not l the 1,000 feet sum from adder 36 mustbe corrected by adding the binary number 1010 thereto. Similarly, if theC carry from adder 35 in unit 32 is not l," the binary number 1010 mustbe added to the feet sum by the correction circuitry in unit 39. At thispoint the one's complement of the deviation setting is added to theeight least significant digits of the sum from addition unit 32 and thebinary number I l l l is added to the four most significant sum digits,that is the 10,000 feet digits, from unit 32. If C is 0, confirmindicator 23 is lit indicating that the aircraft is within the flightcorridor. However, if C is l the descend indicator is immediatelyactivated via AND gate 61. It should be noted that exclusive OR gate 62is inhibited by the coincidence of ls for C and C,,. At this point thealerting system must ascertain whether the upper proximity zone has beenattained, and 2 through 2,, are checked to see whether they are allzeros. If they are not, then this condition alone indicates thatproximity has not been observed. However, if they are all zeros and the100 feet unit can-y C is 0, the binary number 1010 is added to the 100feet sum from adder 53 to yield a valid BCD code. The ones complement ofthe proximity setting is added to the corrected I00 feet unit sum. Theone's complement of the proximity setting is obtained since C, is 1."Next the proximity carry, C,,, from the most significant bit of adder 8!in detection logic unit 71 is monitored. If C, is 0," confirm indicator23 is activated via gate 82 which is inhibited if C,, is l.

A sample computation is included to provide an arithmeticalrepresentation of the binary manipulations performed by 7 the alertingsystem logic units. In the example below, command altitude, deviationand proximity settings are 25. K feet, 0.5K feet and 0.3K feetrespectively. The indicated altitude is 24.8K feet, and with respect tothe other parameters this unreliable analog equipment in'iivhich synchropickoffs were .j

8 the Elimination of periodic adjustments formerly required for used.The digital system is itself errorfree and is limited only by theaccuracy of the altimeter with which it is used. The use wouldcorrespond to a position in the lower approach corridor of thumbwheelswitches for the corridor parameters enable in FIG. 5. The l to theright of the'one's complement of the quick setting and absolute accuracyin selection. command altitude converts it to the twos complement. Thereal advantages of the system lie in its functional sim- 101: 1K 100 i 1Diz t- Digit Digit lmllcqtvtl nltitudn (24.sK 0010 0100 1000 Ono'scomplement of the command altitude (26.5 1101 1010 1010 1 Sum (adders35,36,37) .Q. 0 1111 0 1111 00 c ur Cm 11C sum and 100 surn correctioniact0rsv 0000 0110 sumwmt 32) 1111 1111- 1001 Deviation setting (0.5K).s 0000 0000 0101 znthmuth 2 sum (Unit 47)- 1111 v0 7 1111 1110 100 100sum correction factor- I 0000 Sum (unit 7s)- 1110 Proximity setting (O.3K-)..- 0011 C0 Proximltycarry (g1 0001 v i 9 It should be pointed outthat the application of the alerting system to an altitude problem isjust one use of the system.

Generally speaking, the alerting system'is a general purpose digitalcomparatorwithvariable tolerance settings having LOW, GO or- HIGH OUTPUTsignals. With a proper choice of units, the alertin'g'syst'em can beadapted toother problems such as the accurate positioning of a controlrod'in a nuclear. 'reactona carin a highway lane, or a ship in achannel, or any appropriate system where the control loop is notcompletely closed,-. that is, where a human being, for instance, must Imake-corrections based on data gathered from a display. The

only difference in these applications i'sthe nature ofthe data.

gathering and encoding device which feeds the alerting system logic.Actual implementation ofthe system can be done with NAND and NOR gatesinstead of AND and OR gates. Conversions from AND/OR'arrangements toequivalentNAND/NOR systems are believed toflbe well within the ordinarylevel of skill in the logic design-art. The details-of alternatearrangements with equivalent logic are therefore omitted.

, Instead. of thumbwheel'switches to set in'the control variables,itwould be a-possible alternativetohave remote programming of thecorridor parameters. For example, the command altitude could be changedby radio from the ground by a central computer. responsive to variouschanges in air-traffic patterns. In addition, instead of providing amutually exclusive proximity zone on eitherside of the flightcorridor itwouldbe possible to have overlapping zones by referencing the proximi tysetting directly to the command altitude instead of adding it to thetwo's complement of the deviation setting as in the embodiment describedherein. Another alternative is that the Y command altitude parameterscan be fixed via hard-wiring to provide optimal settings for differenttypes ofaircraft. For example, the deviation and proximity zones couldbe hard-wired leaving the command altitude settable by means of athumbwheelswitch'. Z

Several aspects ofthe logic implementation must be emphasized for theirsimplicity.- For example, the'three basic subtraction operations utilizethe two's complement form. The value of the difference in BCD form neverneeds to begenerated, however. in each case only the carry from themost.

' significant bit is determinative since in two's complement form thisdetermines the sign of the difierence indicating whether the minuend issmaller or larger than-the subtrahend.

I ln addition, the simple manner in which the outputs of deviation andproximity setting units and '73 are manipulated al lows a greatreduction in the size of the logic. I

One of the important advantages gained by this apparatus is plicity.0nce the pilot sets in theassigned or command titude and the desired'proxirnity anddeviation ranges, the operation of the altitude alteringdisplay is completely auto matic until the pilot selects-new parameters.Since the altering system interfaces with existing digital altitudeencoders cur.- rently being incorporated inaircraft, the inventionfacilitates an integral altitude advisory/altering system withoutdegrading 1. An airbomehigh speed altitude alerting sy tem-rm, 1rapidly' substantially simultaneously indicating. the relation! shipsofa digital input signal to a digital reference; level'a'nd to apermissible digital deviation therefrom in either direction defining acorridorc'entered on the reference'level, comprismg: v I

first and second digital-selector means for selecting respec@ 'tively apredetermined reference level and a predetermined permissible deviationand providing respective outputs indicative thereof; 7 v 1 I firstdigitalcomparator means adapted to receive the input greater thereof anda difference output indicative of the magnitude of the difierencebetween the input signal and said first selector means output;

second selector means output andsaid first comparator means differenceoutput for providing a binarysignlout put indicative of the greaterthereof concurrently with provision of said output of said first digitalcomparator;

first logic means responsive to said first and second cbm 9 paratormeans sign 'outputsfor substantially simultaneously providing respectiveoutput signals indicative of whether the input signal is above, below orwithin the corridor.

2.1M alerting system according to claim 1 further comprising:

first fonn; and

said first comparator means including'binary adder means changes in thedetails,

signal and connected to receivesaid'first selector means output forproviding a binary sign output indicative of the I second digitalcomparator means connected to receive said I selectormeans output beingin a complement V adapted ttrreceive the input signal and first selectormeans output for addition thereof to provide said sign output as themost significant carry of said adder means and said difference output incomplement form. 3. An alerting system according to claim 2 wherein:said first selector means output and said first comparator meansdifference output are in twos complement form. 4. An alerting systemaccording to claim 3 further comprising:

said second selector means connected to receive said first comparatormeans sign output for providing said second selector means output intrue form when said first comparator means sign output is in one stateand in complement form when said first comparator means output is in theother state; and said second comparator means including adding meansconnected to receive said first comparator means difference output foraddition thereof to provide said second comparator means sign output asthe most significant carry of said second comparator means adder means.5. An alerting system according to claim 4 further comprissaid firstcomparator means sign output being in the high state when the inputsignal is greater than said first selector means output; said secondselector means providing the complement form of said output in responseto a high said first comparator means sign output; and said first logicmeans including first, second and third gate means each operativelyconnected to receive said first and second comparator means signoutputs, said first gate means providing a decrease signal indicative ofcoincidence of high first and second comparator means sign outputs, saidsecond gate means providing a confirm signal indicative of a highcondition for only one of said first and second comparator means signoutputs, and said third gate means providing an increase signalindicative of coincidence of low first and second comparator means signoutputs. 6. An alerting system according to claim 1 further comprising:

third digital selector means for selecting a predetermined proximityrange on both sides of said corridor and providing an output indicativethereof; said second comparator means further providing a differenceoutput indicative of the magnitude of the difference between said firstcomparator means difference output and said second selector meansoutput; third comparator means connected to receive said secondcomparator means difference output and said third selector means outputfor producing a binary sign output indicative of the greater thereof;and second logic means responsive to said third comparator means signoutput for providing a proximity output signal 55 indicative of whetherthe input signal is adjacent said cor-i I ridor and within saidproximity range substantially simultaneously with provision of saidother output signals. I 7. An alerting system according to claim 4further comprising: i

third digital selector means for establishing a proximity; range on bothsides of said corridor and providing an out-1 put indicative thereof,said third digital selector meansi output being in true form when saidfirst comparator means sign output is in one state and in complementform 65 when said first comparator means sign output is in the otherstate; third comparator means including binary adder means; operativelyconnected to receive said second comparator? means difierence output andsaid third selector means output for producing a binary sign outputindicative of the greater thereof; and second logic means responsive tosaid third comparator means sign output for providing a proximity outputsignal indicative of whether the input signal is adjacent saldcori i lridor and within said proximity range. 8. An airborne high speedaltitude alerting system for rapidly substantially simultaneouslyindicating (1) the level of m a BCD input signal relative to a selectedpredetermined reference level, (2) a permissible deviation therefrom ineither direction defining a corridor, and (3) a proximity rangeimmediately above and below the corridor, comprising:

first digital selector means for selecting the predetermined referencelevel and providing a BCD output in complement form indicative thereofand representing three decimal digits; first binary full parallel addermeans adapted to receive the input signal and connected to receive saidfirst selector means output for providing a binary sign outputindicative of the greater thereof as a most significant carry, and a sum'output, and including means for adding a binary one" to said sum outputfor conversion thereof to binary two's complement form; firstcompensator means connected to receive said first adder means sum outputfor correction thereof to provide a valid BCD output; second digitalselector means connected to receive said first adder means sign outputfor determining the permissible deviation from the reference level todefine the corridor and providing a BCD output indicative thereofrepresenting two decimal digits, said second selector means output beingin true form when said first adder means sign output is in one state andin complement form when said first adder means sign output is in theother state; second binary full parallel adder means connected toreceive said first compensator means output, said second selector meansoutput and said first adder means sign output for adding said firstadder means sign output to each bit of a portion of said firstcompensator means output representing a most significant decimal digitand for adding a corresponding portion of said first compensator meansoutput to said second selector means output to provide a sign output asa most significant carry indicative of whether said first compensatormeans output is greater than said second selector means output; andfirst logic means including first, second and third gate means eachoperatively connected to receive substantially simultaneously said firstand second adder means sign outputs, said first gate means providingwithout appreciable delay a decrease signal indicative of coincidence offirst and second adder means sign outputs in one state, said second gatemeans providing, without appreciable delay, a confirm signal indicativeof said first and second adder means sign outputs having oppositestates, and said third gate means providing, without appreciable delay,an increase signal indicative of coincidence of said first and secondadder means outputs in the other state said signals being providedsubstantially simultaneously. t 9. An alerting system according to claim8 further comprising:

said second adder means further providing a sum output;

of said second adder means sum output representing a least significantdecimal digit for correction thereof to yield a valid BCD output;

third digital selection means connected to receive said first I addermeans sign output for determining a proximity range immediately aboveand below the corridor and providing a BCD output indicative thereofrepresenting a decimal digit, said third selector means output being intrue form when said first adder means sign output is in one state and incomplement form when said first adder means sign output is in the otherstate;

Third binary FIRE; rrTeans connected to receive said second compensatormeans output and said third selector means output for providing a signoutput indicative of the greater thereof; and

second logic means including a pair of gate means each secondcompensator means connected to receive a portion operatively connectedto receive said third adder mean s sign output and a portion of saidsecond adder means output excluding said portion representing said leastsignificantdecimal digit, one'of said gate means providing an secondlogic means OR means output for providing a composite confirm/proximityoutput signal when either thereof is in one state.

11. An alerting system according to claim 9 further comoutput indicativeof coincidence of one state for said third i prising:

adder means sign output and said portion of said second adder meansoutput and the other said gate means providing an output indicative ofcoincidence of the other state l for said third adder means sign outputand said portion of said second adder means sum output, said secondlogic 10 means further including OR means operatively receiving saidpair of gate means outputs for providing a proximity output signal wheneither thereof is in one state.

- inhibit means adapted to receive a signal indicative of a 12. Analerting system according to claim 9 further com- 10. An alerting systemaccording to claim 9 further includ-' 5: r 1 mg. third logic meansincluding OR means operatively receiving said first, second and thirdselector'mesns being BCD thumbwheel switches.

p logic means second gate means output and said m sses

1. An airborne high speed altitude alerting system for rapidlysubstantially simultaneously indicating the relationships of a digitalinput signal to a digital reference level and to a permissible digitaldeviation therefrom in either direction defining a corridor centered onthe reference level, comprising: first and second digital selector meansfor selecting respectively a predetermined reference level and apredetermined permissible deviation and providing respective outputsindicative thereof; first digital comparator means adapted to receivethe input signal and connected to receive said first selector meansoutput for providing a binary sign output indicative of the greaterthereof and a difference output indicative of the magnitude of thedifference between the input signal and said first selector meansoutput; second digital comparator means connected to receive said secondselector means output and said first comparator means difference outputfor providing a binary sign output indicative of the greater thereofconcurrently with provision of said output of said first digitalcomparator; and first logic means responsive to said first and secondcomparator means sign outputs for substantially simultaneously providingrespective output signals indicative of whether the input signal isabove, below or within the corridor.
 2. An alerting system according toclaim 1 further comprising: said first selector means output being in acomplement form; and said first comparator means including binary addermeans adapted to receive the input signal and first selector meansoutput for addition thereof to provide said sign output as the mostsignificant carry of said adder means and said difference output incomplement form.
 3. An alerting system according to claim 2 wherein:said first selector means output and said first comparator meansdifference output are in two''s complement form.
 4. An alerting systemaccording to claim 3 further comprising: said second selector meansconnected to receive said first comparator means sign output forproviding said second selector means output in true form when said firstcomparator means sign output is in one state and in complement form whensaid first comparator means output is in the other state; and saidsecond comparator means including adding means connected to receive saidfirst comparator Means difference output for addition thereof to providesaid second comparator means sign output as the most significant carryof said second comparator means adder means.
 5. An alerting systemaccording to claim 4 further comprising: said first comparator meanssign output being in the high state when the input signal is greaterthan said first selector means output; said second selector meansproviding the complement form of said output in response to a high saidfirst comparator means sign output; and said first logic means includingfirst, second and third gate means each operatively connected to receivesaid first and second comparator means sign outputs, said first gatemeans providing a decrease signal indicative of coincidence of highfirst and second comparator means sign outputs, said second gate meansproviding a confirm signal indicative of a high condition for only oneof said first and second comparator means sign outputs, and said thirdgate means providing an increase signal indicative of coincidence of lowfirst and second comparator means sign outputs.
 6. An alerting systemaccording to claim 1 further comprising: third digital selector meansfor selecting a predetermined proximity range on both sides of saidcorridor and providing an output indicative thereof; said secondcomparator means further providing a difference output indicative of themagnitude of the difference between said first comparator meansdifference output and said second selector means output; thirdcomparator means connected to receive said second comparator meansdifference output and said third selector means output for producing abinary sign output indicative of the greater thereof; and second logicmeans responsive to said third comparator means sign output forproviding a proximity output signal indicative of whether the inputsignal is adjacent said corridor and within said proximity rangesubstantially simultaneously with provision of said other outputsignals.
 7. An alerting system according to claim 4 further comprising:third digital selector means for establishing a proximity range on bothsides of said corridor and providing an output indicative thereof, saidthird digital selector means output being in true form when said firstcomparator means sign output is in one state and in complement form whensaid first comparator means sign output is in the other state; thirdcomparator means including binary adder means operatively connected toreceive said second comparator means difference output and said thirdselector means output for producing a binary sign output indicative ofthe greater thereof; and second logic means responsive to said thirdcomparator means sign output for providing a proximity output signalindicative of whether the input signal is adjacent said corridor andwithin said proximity range.
 8. An airborne high speed altitude alertingsystem for rapidly substantially simultaneously indicating (1) the levelof a BCD input signal relative to a selected predetermined referencelevel, (2) a permissible deviation therefrom in either directiondefining a corridor, and (3) a proximity range immediately above andbelow the corridor, comprising: first digital selector means forselecting the predetermined reference level and providing a BCD outputin complement form indicative thereof and representing three decimaldigits; first binary full parallel adder means adapted to receive theinput signal and connected to receive said first selector means outputfor providing a binary sign output indicative of the greater thereof asa most significant carry, and a sum output, and including means foradding a binary ''''one'''' to said sum output for conversion thereof tobinary two''s complement form; first compensator means connected toreceive said first adder means sum output for correction thereof toprovide a valid BCD output; second digital selector means connectEd toreceive said first adder means sign output for determining thepermissible deviation from the reference level to define the corridorand providing a BCD output indicative thereof representing two decimaldigits, said second selector means output being in true form when saidfirst adder means sign output is in one state and in complement formwhen said first adder means sign output is in the other state; secondbinary full parallel adder means connected to receive said firstcompensator means output, said second selector means output and saidfirst adder means sign output for adding said first adder means signoutput to each bit of a portion of said first compensator means outputrepresenting a most significant decimal digit and for adding acorresponding portion of said first compensator means output to saidsecond selector means output to provide a sign output as a mostsignificant carry indicative of whether said first compensator meansoutput is greater than said second selector means output; and firstlogic means including first, second and third gate means eachoperatively connected to receive substantially simultaneously said firstand second adder means sign outputs, said first gate means providingwithout appreciable delay a decrease signal indicative of coincidence offirst and second adder means sign outputs in one state, said second gatemeans providing, without appreciable delay, a confirm signal indicativeof said first and second adder means sign outputs having oppositestates, and said third gate means providing, without appreciable delay,an increase signal indicative of coincidence of said first and secondadder means outputs in the other state said signals being providedsubstantially simultaneously.
 9. An alerting system according to claim 8further comprising: said second adder means further providing a sumoutput; second compensator means connected to receive a portion of saidsecond adder means sum output representing a least significant decimaldigit for correction thereof to yield a valid BCD output; third digitalselection means connected to receive said first adder means sign outputfor determining a proximity range immediately above and below thecorridor and providing a BCD output indicative thereof representing adecimal digit, said third selector means output being in true form whensaid first adder means sign output is in one state and in complementform when said first adder means sign output is in the other state;third binary full adder means connected to receive said secondcompensator means output and said third selector means output forproviding a sign output indicative of the greater thereof; and secondlogic means including a pair of gate means each operatively connected toreceive said third adder means sign output and a portion of said secondadder means output excluding said portion representing said leastsignificant decimal digit, one of said gate means providing an outputindicative of coincidence of one state for said third adder means signoutput and said portion of said second adder means output and the othersaid gate means providing an output indicative of coincidence of theother state for said third adder means sign output and said portion ofsaid second adder means sum output, said second logic means furtherincluding OR means operatively receiving said pair of gate means outputsfor providing a proximity output signal when either thereof is in onestate.
 10. An alerting system according to claim 9 further including:third logic means including OR means operatively receiving said firstlogic means second gate means output and said second logic means ORmeans output for providing a composite confirm/proximity output signalwhen either thereof is in one state.
 11. An alerting system according toclaim 9 further comprising: inhibit means adapted to receive a signalindicative of a negative value for the input signal and operativelyconnected to said firsT and second logic means for inhibiting said firstlogic means first and second gate means outputs and said second logicmeans OR means output and activating said first logic means third gatemeans increase output.
 12. An alerting system according to claim 9further comprising: said first, second and third selector means beingBCD thumbwheel switches.